Studies of chemical disposition are designed to provide both applied knowledge of the fate of chemicals in the intact animal in support of toxicity tests conducted by the National Toxicology Program and basic knowledge of mechanisms of chemical toxicity. Thus, objectives of these studies are two fold. Each study is designed to address those physical and chemical properties unique to the compound studied as well as to provide data which will permit structural characterization of the respective chemical class. Each study is also designed to address the impact of one or more factors such as dose, age, sex or route of exposure on the toxicity of the chemical(s) studied and the significance of this data to assessments of human health risks. Studies conducted during the current year have addressed the fate and mechanisms of toxicity of 2,2- Bis (bromomethyl)-1,3-propanediol (BMP), a flame retardant, 2- methylimidazole (2-MI) which is widely used in the polymer industry and a series of polychlorinated biphenyls (PCBs). Results of these studies have demonstrated that all of these compounds are readily absorbed, and rapidly distributed to all the major tissues. However, clearance from the body is highly dependent upon polarity and the degree of metabolism. BMP, 2-MI and the more readily metabolized PCBs are rapidly cleared whereas the slowly metabolized PCBs are stored in lipid rich tissues.